Recent innovations in steel making have been directed at making the process more efficient and less burdensome on the environment. One approach has been directed at eliminating the use of the blast furnace. In a conventional steel making process, iron ore is converted to steel in a blast furnace. By first converting the iron ore, which is primarily iron oxide, to iron carbide, the need for using a blast furnace can he avoided. A description of one process for the direct manufacture of steel from iron ore is described in U.S. Pat. No. Re. 32,247. The first step in such a process, called an iron carbide process, is to convert the ore (iron oxide) to iron carbide. In the iron carbide process, the iron oxides are converted to iron carbide in a fluidized bed at low temperatures with a mixture of reducing and carburizing gases such as hydrogen.
An important feature of the iron carbide process involves preheating the reactor feed, comprised of particulate iron oxide and a process gas such as hydrogen, prior to being treated in the fluidized bed reactor. One approach for preheating the reactor feed is described in U.S. Pat. No. 5,137,566. The furnaces previously used for preheating the reactor feed in the processes described in the foregoing patents suffered from the disadvantages of not providing for uniform heating of the tubes or coils transporting the process gas and of not capturing excess heat generated by the furnace. Another disadvantage of prior systems related to inadequate cooling of the flue gas. These and other disadvantages have been overcome by the method and apparatus of the present invention.